It accepted an optional argument to test for equality, but no way
to get the linker language of a particular target.
TARGET_PROPERTY provides this flexibility and STREQUAL provides
the necessary API for equality test.
Extend the CompileDefinitions test to cover accessing the
property of another target.
Since commit e1409ac5 (Support building shared libraries or modules
without soname, 2012-04-22) CMake crashes on the code
add_library(foo SHARED foo.nolang)
because the logic to lookup the language's soname flag was moved from
cmTarget::GetLibraryNames to cmMakefile::GetSONameFlag without its check
for a NULL language. Restore the check for NULL.
Add RunCMake.Languages test to cover language error cases like this one.
Stephen Kelly
Brad King